Automotive fluids, such as engine oil or transmission fluids, absorb heat in use. To prevent fluid deterioration, this heat often needs to be removed. Heat exchangers are commonly used for this purpose. Moreover, heat exchangers are known to perform this function adequately in moderate ambient conditions. However, in cold ambient conditions, engine oils and transmission fluids can be highly viscous. In such conditions, automotive fluids do not flow easily through heat exchangers. Starvation of some downstream components, like transmissions, may even occur. Further, fluid cooling by the heat exchanger when the fluid is already cold is undesirable, as it results in longer warm up time for the engine.
In order to avoid these adverse effects, it is known to provide a mechanism for bypassing the heat exchanger. One way that this has been done in the past is to provide a bypass conduit. The bypass conduit is connected in parallel with the heat exchanger and has a relatively low resistance to the flow of high viscosity fluids as compared to the heat exchanger. Structures of this type are known to avoid starvation of downstream components, but can suffer in that, in normal or warm operating conditions, the flow is split between the heat exchanger and the bypass circuit. This requires that the heat exchangers be made proportionately larger and heavier to achieve the same overall performance for the cooling system. This added size, and weight and the added costs associated therewith, are undesirable to automotive manufacturers.
To ameliorate the split-flow problem, it is known in the prior art to provide bypass valves. Usually, these bypass valves are pressure-activated and are integrally constructed with or attached to the heat exchanger. A heat exchanger exemplary of the foregoing is shown in U.S. Pat. No. 5,499,675 (Haasch et al.), issued Mar. 19, 1996. This structure includes a flapper valve of spring steel biased in a closed position, to arrest bypass flow, and which is adapted to be urged open when the flow resistance through the normal passages of the heat exchanger is too high, as in cold-start conditions. A similar structure is described in U.S. Pat. No. 4,360,055 (Frost), issued Nov. 23, 1982. Heat exchangers of this general type can avoid starvation of downstream lubricated components, and can be adapted such that bypass flow is substantially nil in normal operating conditions, thereby to permit compact heat exchanger construction. However, in Frost, connection of the flapper valve to the heat exchanger typically takes place while the heat exchanger is being mounted to the engine block, using an extension of the oil return pipe. This adds a step in assembly. Rather than simply mounting the oil cooler in place using the oil return pipe extension, the flapper valve must also be interposed. Further complicating assembly is the fact that the flapper valve, being constructed out of fairly lightweight material, is prone to suffering damage until installation, and thus, requires care in handling. Both factors add to assembly costs. In Haasch et al, the flapper valve is also rather delicate and exposed while the heat exchanger is being mounted to the engine block, using an extension of the oil return pipe. The flapper valve is prone to suffering damage or being dislodged during installation. Also, heat exchangers of the Frost and Haasch et al type cannot be modified easily to accommodate different mounting or performance requirements in modern automotive applications.
It is also known to provide heat exchangers including a domed filter plate and a snap-in valve clip. One such structure is described in U.S. Pat. No. 5,544,699 (Robers et al.), issued Aug. 13, 1996. While this structure avoids the loose part problem associated with Frost, special tools are required to install the valve clips, and it is relatively inflexible in use in that a domed filter plate must be utilized, so that it is limited to oil filters of relatively fixed dimensions.